After a year of historic announcements, surprising discoveries and unexpected natural phenomena in 2015, it's hard to say what 2016 will hold for travelers. But we do know that the year ahead will be one of technological innovations and historical significance in many American destinations. Here are the places across the U.S. to keep on your travel radar in 2016.

San Diego

In 2016, San Diego will usher in the future and commemorate its history. The famous San Diego Zoo will be celebrating its 100-year anniversary all year with new exhibitions and events for both locals and visitors. South of the zoo, America's first bi-national airport will open and allow travelers flying through Tijuana International Airport to cross over to San Diego without ever leaving the airport.

A 390-foot foot-bridge, known as the Cross Border Xpress, crosses over the fence that separates the U.S. from Mexico, which will save travelers from waiting in the traffic of the border crossing. It costs $18 and takes five minutes to walk across the overpass to a U.S. border inspector. This innovative approach to border crossings is more convenient and great news for travelers wishing to explore both Tijuana and San Diego.

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Vehicles pass under a walking bridge that connects the new Cross Border Xpress air terminal in San Diego, right, to the Tijuana International Airport, left, in this file photo taken in Tijuana, Mexico, on Nov. 25, 2015. The new terminal is scheduled to begin operations on Wednesday, Dec. 9.
Lenny Ignelzi, AP

A security inspection station is seen at the Cross Border Xpress air terminal in San Diego on Nov. 25, 2015. The new terminal, with a bridge that crosses to Tijuana, Mexico's decades-old airport, is scheduled to begin operations on Wednesday, Dec. 9, 2015.
Lenny Ignelzi, AP

The courtyard entrance to the Cross Border Xpress air terminal shows displays the design of renowned Mexican architect Ricardo Legoretta in San Diego in this photo from Nov. 25, 2015.
Lenny Ignelzi, AP

Enrique Valle, CEO of the Cross Border Xpress air terminal, along with Elizabeth Brown, the chief commercial officer of CBX, talks about the business plans for the terminal in San Diego in this photo from Nov. 25, 2015. The new terminal, with a bridge that crosses to Tijuana, Mexico's decades-old airport, is scheduled to begin operations on Wednesday, Dec. 9.
Lenny Ignelzi, AP

The walking bridge is shown at the Cross Border Xpress air terminal in San Diego on Nov. 25, 2015. The terminal, which uses the bridge to connect to Tijuana, Mexico's decades-old airport, is scheduled to begin operations on Wednesday, Dec. 9.
Lenny Ignelzi, AP

An escalator at the Cross Border Xpress air terminal shows displays the design of renowned Mexican architect Ricardo Legoretta in San Diego in this photo from Nov. 25, 2015. A new terminal in San Diego with a bridge that crosses to Tijuana, Mexico's decades-old airport, is scheduled to begin operations on Wednesday, Dec. 9.
Lenny Ignelzi, AP

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Whether it's your first, second or hundredth time, 2016 is the year to visit Louisville. The Urban Bourbon Trail has expanded with the opening of seven new distilleries offering bourbon, brandy and moonshine.

But bourbon isn't the only thing Louisville has brewing. The Mega Cavern is an underground bike park with more than 320,000 square feet of trails, jumps and BMX tracks. All this has been constructed in a limestone cavern 100 feet below the surface.

The Mega Cavern isn't just for extreme athletes, though. It offers trails for riders of all ages, with or without training wheels. You can also enjoy the ropes course, tram car and zip-lines. Plus, with the absence of rain, no need for sunscreen, and a climate-controlled temperate of 60 degrees Fahrenheit, biking underground has a lot of advantages. This is one adventure vacation that won't be ruined by the weather.

The national parks

The U.S. National Parks Service will officially celebrate its 100th anniversary on Aug. 25, but you won't have to wait until then to enjoy this special event because the parks will be celebrating throughout the year. The National Park Service has launched the Find Your Park campaign to help travelers find the national parks closest to them. And with more than 400 parks, there's a lot to explore locally and across the country.

The parks will be also be free on the following days in honor of the centennial:

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The Spanish Missions of San Antonio were officially named a UNESCO World Heritage site in July 2015. These religious outposts are landmarks of the Spanish Empire and hold great historical value. You may remember the Alamo, but there are many more missions to discover south of the city, some of which you can even explore by kayaking along the San Antonio River.

Along this river, you'll see and enjoy the native vegetation that has been restored and is thriving after years of settlement took a toll on the environment. History is also thriving within the city center with the opening of the Emma Hotel and the tastings and tours that are offered at the city's historic Pearl Brewery.

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Besides the more famous Alamo – actually a nickname for the historic Mission San Antonio de Valero – four other missions clustered around the San Antonio River are being recognized as the largest collection of Spanish colonial architecture north of the Rio Grande, and one of the largest collections of Spanish missions anywhere in the world.
San Antonio Convention & Visitors Bureau

Each has its own architecture, its own essence and its own story, and each, except for the Alamo, is the home of an active parish. Shown here is Mission San Jose.
San Antonio Convention & Visitors Bureau

In the past several years, Bexar County and the San Antonio River Authority joined with the federal government and other agencies to carry out a $358 million river restoration project. The River Walk was expanded from 3 to 15 miles.
San Antonio Convention & Visitors Bureau

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If you're planning on celebrating the National Park's Centennial, a trip to Hawaii Volcanoes National Park is a must. As the 15th national park to be established in the U.S., the park will be celebrating all year long by introducing a Centennial Hike series, After Dark programs and more. This is a wonderful chance to take in the spectacular geology of the region and learn how the many eruptions have changed Volcanoes National Park over the past 100 years. And if you're the athletic type, you might consider taking part in the Ragnar Relay, an overnight race that's sweeping the country and coming to Hawaii in 2016.

Oklahoma City

The Oklahoma City Boathouse District is where Olympic kayakers and canoeists train, and now the facilities will be opening up a brand new state-of-the-art adventure facility for the public in 2016. RIVERSPORT Rapids will be one of the only aquatic adventure facilities in the world that's fit for both Olympic athletes and families.

And when you've conquered the river, stay tuned for H&8th Oklahoma City's popular food truck market that features live music, local beer and more than 45,000 people. In 2016 the market will switch from monthly to yearly in order to make it bigger and coincide with the Pro-am bike races.

The year ahead will also see the opening of The Criterion, a new music venue in the Bricktown neighborhood.

Philadelphia

The City of Brotherly Love heads into 2016 with a new title under its belt: America's first UNESCO World Heritage City. Visitors will be able to take in expansive views of the city from the new One Liberty Observation deck, the Philadelphia Museum of Art will be hosting international art exhibitions throughout the year, and the city will also host this year's Democratic Convention, which is sure to amplify Philly's already patriotic buzz.

Cleveland

For Cleveland, 2016 is the year of the pedestrian. With the renovation of a greener Public Square underway and plans to build restaurant and retail spaces in both Edgewater Park and the Flats East Bank District, there will be more to do on foot in Cleveland than ever before. It's a great year to take in the sights along the Cuyahoga River or explore the beaches of Lake Eerie while enjoying this friendly and accessible city.

Daytona, Fla.

Daytona is revving up its engines for the completion of the immense Daytona Rising. The overhaul of Daytona International Speedway is set to open in January and will be packed with amazing new features for racing enthusiasts. There are 11 new social areas, 60 new luxury trackside suites, and 101,000 new grandstands featuring arm and back rests. And with the installation of more than 5,000 solar panels, Daytona Rising will simultaneously thrill fans and conserve energy.

Indiana

The state of Indiana is celebrating a notable moment this year with the commemoration of its bicentennial. And as everyone knows, there's no party like a 200th birthday party. Special events throughout the state include summer symphonies on the beach and a sand sculpture contest at Indiana Dunes State Park. Indiana's many microbreweries will also be joining the festivities by coming together to create a special bicentennial brew. 2016 will also signify the 100th running of the Indy 500.

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Indiana, the 19th state of the Union, is a little bit of everything: rural (Amish country) and cosmopolitan (Indianapolis), serene (Tibetan temples) and fast-paced (the Indy 500). No one knows for sure why it's called the Hoosier State, but it's inarguably a unique and often surprising destination.
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Indianapolis, the most populous city in Indiana, strikes a perfect balance between its sports-loving culture and an appreciation for the arts. Its outdoor spaces, particularly the Urban White River State Park (pictured), make it one of the Midwest's most vibrant cities.
Visit Indy

The Indiana State Capitol, located in Indianapolis, is one of only a handful of state government buildings in the nation where all three branches of the government operate. The building, completed in 1888, features a stunning stained glass rotunda window made from German glass.
Getty Images/iStockphoto

Young (and young-at-heart) visitors to Indiana will find the world's largest children's museum in the state capital. The Children's Museum of Indianapolis features five floors of interactive exhibits, including a sizable collection of dinosaur fossils.
Lavengood Photography

Located in the harbor of Michigan City on Lake Michigan, the Michigan City East Light is one of the area's most recognizable landmarks and one of the few Great Lakes lighthouses with an iron walkway above the pier.
Indiana Office of Tourism Developmen

Lively Bloomington, located 53 miles south of Indianapolis, is home to Indiana University and a very walkable (or bike-able) town center packed with restaurants, boutiques, college bars and bookstores.
Visit Bloomington

On Lake Michigan's southern shore, Indiana Dunes State Park protects more than three miles of sandy beach and rolling dunes, which attract swimmers, hikers, cyclers and campers throughout the warmer months.
Joseph Lax-Salinas, Getty Images/iStockphoto

Funky and eclectic Fountain Square, a neighborhood located just southeast of downtown Indy, is a one-stop destination for antique shopping, art galleries, live music and one-of-a-kind shopping. The historic Fountain Square Theatre, built in 1928, got its start as a vaudeville and motion picture theater.
Lavengood Photography

Indiana is most certainly a sports-loving state, but no event here is more iconic than the annual Indy 500. The Greatest Spectacle in Racing takes place each year at the historic Indianapolis Motor Speedway and has become the largest single-day spectator sporting event in the world.
Indianapolis Motor Speedway

The Midwestern United States might not be the first place you'd think to look for Tibetan Buddhist culture, but Bloomington is actually home to a Kalachakra Stupa, a monument dedicated to the Dalai Lama in 1999 as a symbol of world peace.
Visit Bloomington

At the 26-acre Lilly House & Gardens, visitors can tour the former mansion of J.K. Lilly Jr., an Indianapolis philanthropist and businessman. The home, restored to how it looked in its 1930s glory days, now functions as a historic house museum.
Indianapolis Museum of Art

The Round Barn Theatre at Amish Acres, housed within a round barn from 1911, is home to a professional theater company who perform musicals from Broadway's golden age. They've put on over 100 productions to date.
Indiana Office of Tourism Development

Cataract Falls in Owen County includes the largest waterfall by volume in the state of Indiana. The Upper Falls (pictured) drop 20 feet, while the Lower Falls further downstream plummet 18 feet.
Kenneth Keifer, Getty Images/iStockphoto

Professional baseball is returning to Hartford for the first time in 60 years, and in 2016 the city will have both a new minor league team and a new stadium — Dunkin Donuts Park. The complex, set to open for the 2016 season, will include a supermarket and the relocated Thomas Hooker Brewing Company. Additionally, new hotel openings, such as Hotel@440 and Delmar West Hartford, are adding to city's 2016 buzz.

Detroit

Detroit is a rapidly changing city. In 2016, it's all about learning and family fun with the opening of a new Legoland, a comprehensive Beatles exhibit, and an expansion to the Sea Life Michigan Aquarium.

Also set to open early in 2016, the Polk Penguin Conservation Center will be the largest penguin facility in the world. Visitors will have the opportunity to observe four different species of penguin play, dive, and fish in their aquatic habitat.

Las Vegas

It will be a year of anniversaries and music in Sin City as Ceasars Palace celebrates its 50th anniversary with the opening of the renovated Julius Tower. In August, Celine Dion will come to the Palace to perform her 1,000th show. Also in 2016, Jennifer Lopez and Lionel Richie will both begin their residency at The AXIS at Planet Hollywood.

Galveston, Texas

If you're looking for an exciting summer vacation, look no further than this island off the coast of Texas. Galveston will become the newest port for Carnival Cruise Lines and will host the Carnival Breeze in the Port of Galveston on May 8. Disney Cruise Line will also sail from the island this year. Even if you don't take to the seas, there's never been a better time to visit Galveston. After a beach nourishment and expansion project, the city is ready to unveil seven miles of new beach by spring break.